In recent years, surround-sound systems for amplifying the sounds of human voices, music and the like have been put into practical use. Each of those surround-sound systems has a plurality of speakers including a center speaker, left and right front speakers and left and right rear speakers each having a specific function of reproducing sounds such as adding reverberant sound and changing the frequency characteristics.
As a typical surround-sound system, a 5.1 ch (channel) surround-sound system of the Dolby Digital (a registered trademark) that is formed with a center speaker placed in front of a listener, front speakers placed on the left and right sides of the center speaker, surround speakers placed on the left and right rear sides or left and right sides of the listener, and a sub woofer for exclusively amplifying low-frequency sounds of lower than 120 Hz is known to the public.
Meanwhile, a reproducing system that has an array speaker formed with speaker units having the same characteristics including performance has recently been known. Such a reproducing system drives and controls the speaker units independently of one another, so as to control the directivity of each sound amplified through the array speaker.
This reproducing system includes an array speaker formed with speaker units, and a sound reproducing apparatus that has finite impulse response (FIR) filters for inputting audio signals branching from one signal source and drives the array speaker. The reproducing system is arranged to set the filter characteristics of each of the FIR filters by a nonlinear optimization technique, so that the directivity of each sound amplified through the array speaker has a desired directivity. With this configuration, the reproducing system can control the directivity for each frequency band from a low frequency band to a medium high frequency band (see Patent Document 1, for instance).
Patent Document 1: Japanese Patent No. 2610991